1. Field of the Invention
The present invention relates to a power device and a manufacturing method thereof, and more particularly, to a power device that is capable of performing a normally-OFF operation.
2. Description of the Related Art
A semiconductor light emitting device (LED) is a semiconductor device that generates various colored lights based on the re-bonding of an electron and a hole at a P-N junction when a current is applied. Demand for the semiconductor LED has been continuously increased since the semiconductor LED has many advantages, such as, a long lifespan, a low power consumption, a fast start-up, a high vibration resistance, and the like, when compared to a filament-based LED. Particularly, a nitride semiconductor that emits a blue light, in a short wavelength range, has drawn attention.
As information communication technologies have been considerably developed globally, communication technologies for high-speed and large-capacity signal communication have been rapidly developed. Particularly, as demand for a personal cellular phone, a satellite communication, a military radar, a broadcasting communication, a communication relay, and the like in wireless communication technology has increased, the demands for a high-speed, a high-power electronic device required for a high-speed information communication system of a microwave band and a millimeter-wave band have increased. Also, research on a power device used for a high-power have been actively conducted to reduce energy loss.
Particularly, since the nitride semiconductor has advantageous properties, such as a high energy gap, a high heat stability, a high chemical stability, a high electronic saturation velocity of about 3×107 centimeters per second (cm/sec), the nitride semiconductor may be readily utilized as an optical element, and a high frequency and high power electronic device. Accordingly, research on the nitride semiconductor is being actively conducted the world over. An electronic device based on the nitride semiconductor may have varied advantages, such as, a high breakdown field of about 3×106 volts per centimeter (V/cm), a maximum current density, a stable high temperature operation, a high heat conductivity, and the like.
A heterostructure field effect transistor (HFET) generated based on a heterojunction of compound semiconductors has a high band-discontinuity at a junction interface, a high-electron density may be freed in the interface and thus, an electron mobility may increase. However, in an aluminum gallium nitride (AlGaN)/gallium nitride (GaN) HFET structure having a high electron mobility, a current flows even in a state where a signal is not applied and thus, power is consumed.
Since a power device may require a high current density, a power loss in a normally-ON device may be a great drawback. Accordingly, a normally-OFF device that embodies a metal-oxide semiconductor (MOS) HFET by removing an AlGaN layer from a gate portion has been developed. The normally-OFF device may form a recess structure by removing the AlGaN layer from the gate portion using an inductively coupled plasma-reactive ion etch (ICP-RIE) scheme, may embody the MOS HFET using an insulating material as a gate oxide, and may form a channel by applying a voltage. However, the normally-OFF device may have difficulty in accurately controlling a thickness of the AlGaN layer, and may have a drawback of deterioration in electrical properties when a surface is exposed to plasma while using the ICP-RIE scheme.